1. Field of the Invention
The present invention relates to an inkjet printing apparatus, an inkjet printing method and an inkjet printing system. Particularly, the present invention relates to an inkjet printing apparatus that performs printing by reciprocally scanning a printing medium using printing heads that discharge inks of a plurality of different types, and an inkjet printing method and an inkjet printing system.
2. Description of the Related Arts
The serial type inkjet printing apparatuses produced today are widely accepted and employed by the general public, primarily because they are compact and are relatively low priced, a result of their comparatively inexpensive designs and construction. These serial type inkjet printing apparatuses are designed to sequentially form images on a printing medium by alternately conveying the printing medium and scanning it with a printing head.
FIG. 2 is a schematic perspective view provided for explaining the arrangement of a serial type inkjet printing apparatus. Reference numberal 22 is a collective designation for six color printing heads, 22K, 22LC, 22C, 22LM, 22M and 22Y, for respectively discharging ink in the colors black (K), light cyan (LC), cyan (C), light magenta (LM), magenta (M) and yellow (Y). As shown in FIG. 2, the six color printing heads 22 are arranged in the main scanning direction (a direction indicated by an arrow B).
Upon receiving a printing start instruction, the printing heads 22, positioned as shown in FIG. 2 (at a home position), move across (scan) a printing medium 1 in the direction indicated by the arrow B (in the forward scanning direction), while simultaneously printing, as shown in FIG. 13, a belt-like image area (a band) having a width corresponding to the array range of the discharge ports in the printing heads 22. While scanning in the forward scanning direction (forward scanning) is being performed, ink is deposited on the printing medium 1 in the order black, light cyan, cyan, light magenta, magenta and yellow. Then, when the printing of one scan (one band) has been completed, to prepare for the printing of another band, a conveying roller 3 is rotated to convey the printing medium 1 a predetermined distance in the direction indicated by an arrow A in FIG. 1B. This time the printing head unit 2 deposits ink while moving back toward the home position (in the reverse scanning direction indicated by the arrow B) and prints another band. During the reverse scanning, the order in which ink is deposited on the printing medium 1 is the reverse of that in which it is deposited during the forward scanning, i.e., in the order yellow, magenta, light magenta, cyan, light cyan and black. Then, during a period following the completion of the most recent scanning and before the next scanning is started, the conveying of the printing medium 1 is performed by the rotation of the conveying roller 3. When the above described operation for the scanning of a band and the conveying of a printing medium a predetermined distance is repeatedly performed, a desired image can be formed on the printing medium 1.
Recently, as one means for improving the work efficiency of printer users, there have been requests for further increases in printing speeds. However, since most inkjet printing apparatuses employ water-based liquid inks, a specific fixing period is required to permit ink deposited on a printing medium to dry. This fixing period is required because when the ink in a printing area is not completely dry and it is overlapped by another printing medium, the printing area is smudged and so-called smearing occurs. Therefore, when seeking to increase printing speeds, the resolution of the smearing problem is an important problem.
Several solutions for reducing smearing have been proposed (Japanese Patent Laid-Open Publications No. 07-205416, No. 11-309847 No. 2002-337319 and No. 08-112893).
In Japanese Patent Laid-Open Publication No. 07-205416, disclosed is a method whereby a high density printing area on the most recently printed page is detected, and a period during which a subsequent page is to be kept from contacting this printing area is determined. Then, the printing of the following page is delayed until the fixing of the printing area on the preceding page has been completed, so as to prevent the following page from contacting the printing area during the determined period of time. According to this method, if the fixing of the high density printing area has been completed, the printing of the following page that will contact it is not delayed. On the other hand, if the fixing of the high density printing area has not been completed, the printing of the following page is delayed.
In Japanese Patent Laid-Open Publication No. 11-309847, disclosed is a technique whereby, in addition to the configuration described in Japanese Patent Laid-Open Publication No. 07-205416, the area of the following page for which printing is to be delayed is changed in accordance with the printing ratio for the following page.
In Japanese Patent Laid-Open Publication No. 2002-337319, disclosed is a technique whereby, in addition to the configuration described in Japanese Patent Laid-Open Publication No. 07-205416, the timing for the delay in the printing of the following page is changed in accordance with the sheet size of the following page.
In Japanese Patent Laid-Open Publication No. 08-112893, disclosed is a method for setting a specified period in accordance with the type of printing medium. Then, as a succeeding printing medium is being conveyed within the specified period, either the printing operation or the conveying of the printing medium is halted, so that the succeeding printing medium, which is yet to be discharged. is prevented from contacting the previously discharged printing medium.
When one of these methods is employed, an image can be printed for which the possibility of smearing is reduced, while a major control mechanism is not especially required for the printing apparatus and the printing speed is not reduced more than is actually necessary.
Recently, in order to improve both the quality of black characters and the quality of a color photographic image, many inkjet printing apparatuses have been provided in which black ink and color inks having different properties in permeation and diffusion can be mounted. For example, a printing apparatus is provided wherein a pigment is employed as black ink and dyes are employed as other color inks, and an inkjet printing apparatus is provided that employs low permeant black ink and high permeant ink in other colors. Furthermore, in order to improve the quality of a printed image, an inkjet printing apparatus is also provided wherein a liquid that reacts with ink is mounted, or wherein a plurality of inks that react with each other are mounted (see Japanese Patent Laid-Open Publication No. 2002-307671). In this case, ambiguity (e.g., feathering) at the edges of black characters and color bleeding are prevented, as is excessive permeation of printing medium by ink. As a result, a high quality, high density images can be obtained.
When the above described different types of ink (or liquids) are mounted in a serial inkjet printing apparatus, as shown in FIG. 2, and bidirectional printing is performed, the order in which ink is provided differs for forward scanning and for reverse scanning. And in such a case, according to a study performed by the present inventors, it was found that there is a difference in the fixing times required for an image printed during forward scanning and an image printed during reverse scanning.
The methods described in the above patent documents, however, do not take into account the resultant difference in fixing times when the order in which ink is provided differs. Therefore, when the methods described in these patent documents are applied, periods that is longer than necessary are required to resolve smearing. That is, for an image printed using both forward scanning and reverse scanning, the printing process must be adjusted to prevent smearing in the portions of the image that require longer fixing times. Therefore, in the interest of providing shorter printing times, further improvements are required.